Help & troubleshooting for channels on your Roku device, including adding/removing channels, logging in to, authenticating, or activating a channel, channel-specific playback issues, assistance contacting channel publishers to report issues, and adjusting channel-specific settings.
The only way is to have separate Roku accounts for you and your children and then you can add a PIN to their account so that they can't make purchases or add channels. Any channel/app added or removed from one device will be added or removed from all devices linked to the same account. One of the downsides of separate accounts is that anything paid through Roku will only be available on one device or the other. That's just one reason why it's always better to subscribe directly through the provider and not through Roku.
Roku Community Streaming Expert
Help others find this answer and click "Accept as Solution." If you appreciate my answer, maybe give me a Kudo.